The present invention relates to making three-dimensional objects, such as models, dies, molds and the like by bonding together a large number of relatively thin layers, each containing the contour of a thin slice of the object and, in particular, it concerns a method and apparatus for bonding the sheets together without trapping bubbles between two adjacent sheets and a procedure for easy detachment of the stack of bonded together sheets upon completion of the three-dimensional object. In practical usage, the terms adhere, bond, glue and their respective grammatical derivations are considered to be synonymous, and may therefore be used interchangeably herein.
The entrapment of air-bubbles between two planar surfaces when they are bonded together is a well-known phenomenon that may cause non-uniform bonding of the layers, thus weakening the bond.
Application specific solutions have been suggested. WO9943490 to Oehman, for example, discloses a method for gluing optical disc substrates together, by holding the substrates coaxially in a horizontal attitude, introducing liquid adhesive to a central region of the gap between them and rotating the discs rapidly while bringing them together.
The problem of bonding without air bubbles is exacerbated when sequentially adhering sheets together due to lack of planarity in different regions of the top surface of the stack. This lack of planarity is due to varied thickness of the stack in different regions, caused by sheet manufacturing production tolerances, or uneven spreading of adhesive between the sheets.
Attempts to solve the problem of trapped air bubbles when building a three-dimensional object on a planar surface consider the seemingly contradictory requirements of providing a stable structure for the accumulated layer-by-layer construction while enabling easy removal of the bonded stack containing the three-dimensional object from the stable structure once it is complete.
There is therefore a need for a method and device for adhering subsequent sheets to a stack without trapped bubbles while providing a mode for the easy removal of the finished stack from the mechanism that created the stack.